Genes Are Not Destiny
Summary: Genes specify context-dependent tendencies, not outcomes. The correct question is never “what does this gene do?” but “what does this gene do in this environment with this network of other genes?” The effect of any single gene on behavior is typically tiny.
Sources: Sapolsky-Behave.md · Klaas-Fluke.md
Source pages: Fluke: Chance, Chaos, and Why Everything We Do Matters — Quotes, Behave: The Biology of Humans at Our Best and Worst — Quotes
Last updated: 2026-04-26
The misconception
The popular framing — “the gene for X” — is almost always wrong. For height (a far simpler trait than behavior), hundreds of genetic variants were identified in GWAS studies; the single most powerful explained 0.4% of variance. Behavior is more complex than height.
“Having the ‘warrior gene’ variant of MAO probably has less effect on your behavior than does believing that you have it.” (source: Sapolsky-Behave.md)
Context-dependence
“Ask not what a gene does. Ask what it does in a particular environment and when expressed in a particular network of other genes (i.e., gene/gene/gene/gene…/environment).” (source: Sapolsky-Behave.md)
The DRD4 7R variant — associated with novelty-seeking, extroversion, and impulsivity — illustrates this: it is present in ~23% of Europeans but only ~1% of East Asians. The difference is not random; populations that domesticated rice ten thousand years ago selected against 7R because tight cooperation was required. The gene’s expression was shaped by ecological and cultural context over millennia. See collectivist-vs-individualist.
The same variant can predict either impulsive theft or impulsive generosity — the gene shapes magnitude of response, not its valence.
“Genes aren’t about inevitability. Instead they’re about context-dependent tendencies, propensities, potentials, and vulnerabilities.” (source: Sapolsky-Behave.md)
Polygenic complexity
Virtually all behavioral traits are polygenic — influenced by hundreds or thousands of variants, each with tiny effect. Gene-environment interactions make simple prediction impossible: a variant associated with aggression in high-stress environments may have no effect or opposite effects in low-stress ones.
Connection to Klaas
Klaas-Fluke argues that contingency — the sensitivity of outcomes to initial conditions and random events — is the fundamental character of history and biology. This is the macro-level version of the same point: outcomes that appear inevitable in retrospect were highly sensitive to conditions that could have been otherwise. See narrative-bias.